Asphalt-based roofing materials, such as roofing shingles, roll roofing and commercial roofing, are installed on the roofs of buildings to provide protection from the elements, and to give the roof an aesthetically pleasing look. Typically, the roofing material is constructed of a substrate such as a glass fiber mat or an organic felt, an asphalt coating on the substrate, and a surface layer of granules embedded in the asphalt coating.
A common method for the manufacture of asphalt shingles is the production of a continuous sheet of asphalt material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphalt sheet material, either a glass fiber mat or an organic felt mat is passed through a coater containing hot liquid asphalt to form a tacky, asphalt-coated sheet. Subsequently, the hot asphalt-coated sheet is passed beneath one or more granule applicators which discharge protective and decorative surface granules onto portions of the asphalt sheet material.
In the manufacture of colored shingles, two types of granules are typically employed. Headlap granules are granules of relatively low cost used for the portion of the shingle which will be covered up on the roof. Colored granules, prime granules, or other reflectivity-increasing granules are of relatively higher cost and are applied to the portion of the shingle that will be exposed on the roof. In some applications, specialized granules that provide increased solar heat reflectance to reduce the solar absorption of the shingle may be used. For example, U.S. Published Patent Application No. 2005/0072114, entitled “Colored Roofing Granules with Increased Solar Heat Reflectance, Solar Heat-Reflective Shingles, and Process for Producing Same,” the entire disclosure of which is incorporated herein by reference, discloses colored infrared-reflective roofing granules that provide increased solar heat reflectance.
One of the problems with conventional granule application methods for manufacturing laminated shingles is that the underlay will be covered by the relatively more expensive prime granules. In such conventional methods for manufacturing laminated shingles, even the portions of the underlay that will be covered by the tabs of the overlay are covered with prime granules.
Further, asphalt shingles are commonly produced from a continuous sheet of traditional, black asphalt material followed by a shingle cutting operation which cuts the material into individual shingles. When granules are discharged onto the black asphalt sheet, the granules do not cover the entirety of the shingle and the asphalt will be exposed on the roof. As a result, the exposed traditional, black asphalt will absorb solar heat.